The present invention is in the field of multiple photoflash lamp arrays, such as flashcubes and planar arrays, adapted to be temporarily attached to a camera capable of producing a plurality of flashes for taking a plurality of pictures. In general, these multiple photoflash arrays or assemblies comprise a reflector unit having a plurality of adjacent reflector cavities, each having a photoflash lamp mounted therein and are well known in the art.
The conventional flashcube is one well-known embodiment of such photoflash lamp arrays and an example of a flashcube is described in the U.S. Pat. No. 3,739,166 to R. M. Anderson. Various type linear or planar photoflash arrays are also well-known in the art wherein a series of reflectors are arranged in one or more rows which may face in the same direction to form a single-sided array or in opposite direction to form a two-sided array. An example of such two-sided array is described in the U.S. Pat. No. 3,598,984 whereas such single-sided array is described in the U.S. patent application entitled "Multiple Photoflash Lamp Unit", of K. H. Weber, Ser. No. 448,671, filed Oct. 22, 1973, now Pat. No. 3,937,946 and assigned to the assignee of the present invention.
As further illustrative of the various designs and constructions that have already been proposed for multiple lamp photoflash arrays, it is known to have associated flashlamp-reflector assemblies mounted adjacent to one another in one or more rows facing in the same direction and operatively associated with electrical circuit means so that a group of the flashlamps which are relatively further from the camera lens axis than are the other lamps of the unit will be flashed. This mode of operation can be accomplished with a lamp configuration in which the individual flashlamps are electrically connected to a printed circuitboard member with electrical contact being made to the camera by contact tabs located at the opposite ends of the circuitboard which readily plug into a suitable receiving socket on the camera itself or to an adaptor thereto. An electrical energy source which may be contained within the camera is connected to said contact tabs so that a firing pulse produced by the source can be applied across said contacts depending upon the type of lamps used in the flashlamp array. If low voltage filament type flashlamps are employed in the array, the firing pulse source may be of the battery or battery-capacitor discharge type producing in synchronization with opening of the camera shutter, a pulse of approximately 3 volts to 15 volts or more and of sufficient energy to fire a single flashlamp. An example of suitable low voltage flashlamp is disclosed in U.S. Pat. No. 3,506,385 to K. H. Weber and G. W. Cressman and an example of a low-voltage flash-sequencing circuit is disclosed in the U.S. Pat. No. 3,532,931 to P. T. Cote' and J. D. Harnden. If the flashlamps in the multiple flash array are of the so-called high-voltage type, requiring a pulse of approximately 1,000-2,000 volts, the firing pulse source may comprise a suitable battery-capacitor discharge and voltage step-up transformer type circuit, or may employ a compact piezoelectric element arranged to be impacted or stressed in synchronization with opening of the camera shutter, so as to produce a firing pulse having a voltage of approximately 1,000 or 2,000 volts and of sufficient energy to fire a single flashlamp. An example of a high-voltage flashlamp and a firing pulse source comprising a piezoelectric element synchronized with the camera shutter described in U.S. Pat. Nos. 2,972,937 and 3,106,080, both to C. G. Suits.
Radiation switches which are suitable in a flash sequencing circuit of the type above generally described are also known. The switches which can be employed in various ways are converted from a high resistance or open circuit condition upon flashing of an adjacent flashlamp in the array to provide a low resistance circuit path to another unflashed lamp. An already known solid switch material composition which provides greater humidity resistance at above normal ambient temperatures and operates in this manner is described and claimed in U.S. patent application, Ser. No. 508,105, filed Sept. 23, 1974and now abandoned, entitled "Switching Devices for Photoflash Unit", in the names of R. L. Smialek and M. S. Jaffe, and assigned to the assignee of the present invention. The particular switch material composition described in said patent application comprises a mixture containing a silver source and a humidity resistant organic polymer binder which further contains a small but effective amount of a stabilizer additive forming an insoluble reaction product with silver ion.
A technique is also described in U.S. Pat. No. 3,451,813 to L. C. Kinney et al. for producing a printed circuit by forming a pattern of a photoflash sensitive conducting metal precursor such as silver oxide, copper oxide, nickel formate, or copper powder on a substrate and photoflashing high intensity radiation for a short duration such as 0.2 to 30 milliseconds onto the pattern to convert it to a coherent conducting metal circuit adherent to the substrate. Since the source material which can be converted to an electrically conductive state in this manner is said to include metals and metal compounds which are already electrically conductive, it is apparent that such mixtures which further can contain an organic polymer binder would not prove suitable as a static solid switching device in a flashlamp sequencing circuit. Said technique can further require multiple photoflashes to provide electrical conductivity when a copper source material is converted to a metallic copper deposit which would not be suitable in a flashlamp sequencing circuit operating in the manner above generally described. Still other electrically conductive reducing agents and fluxing agents are recommended as additives to the already electrically conducting and semi-conducting metal precursor materials being utilized and in amounts which could render such material compositions entirely inoperative in switching from a high resistance to a low resistance only when activated by actinic radiation.
In the aforementioned concurrently filed U.S. patent application Ser. No. 520,967, there is disclosed a switch material composition which is suitable in a flash sequencing circuit of the type above generally described which comprises a mixture of finely divided cupric oxide with a humidity resistant organic polymer binder. Useful cupric oxide material is maintained below an average particle size of 1 micron to provide the desired flashing sensitivity of operation with existing flashlamp constructions. The desired conversion of cupric oxide to elemental copper takes place with accompanying combustion of the organic binder in the preferred switch material compositions by further maintaining stoichiometric proportions between cupric oxide and the binder in the mixture. The switches have also been found to exhibit improved shelf life under conditions of relatively high humidity at above normal ambient temperatures.